Many noble metal materials are used in a metal wiring in a semiconductor device. The noble metal material is defined as a generic term of groups 10 and 11 in the periodic table. Particularly, gold, platinum, or the like is formed as a functional material by a sputtering method (hereinafter also referred to as “sputtering”) due to its productivity and easiness. In Patent Literature 1, for example, platinum film-formed by sputtering is used in an electrode. As sputtering, plasma sputtering using plasma is widely used.
The behavior of particles during the plasma sputtering will be explained using FIG. 4. The plasma during sputtering includes ions of a gas introduced as a discharge gas and a metal ion 603 emitted from a target 608. These ions 603 are accelerated by an electric field and enter the target 608 attached to a cathode 601, and a secondary electron 604 is emitted on a surface of the target 608. Since some ions 603 have a momentum obtained by, for example, particle collision, they collide against an inner wall of a discharge space. In a common sputtering apparatus, in order to prevent a chamber inner wall of the discharge space from being covered by sputtering particles, a deposition preventive board 602 is provided to be mounted inside the chamber inner wall; therefore, the inner wall of the discharge space may be referred to as a surface of the deposition preventive board 602. Also on the surface of the deposition preventive board 602, the secondary electron 604 is emitted by the collision of the ion 603 as on the surface of the target 608, and the plasma is maintained by electrons continuously supplied from each surface of the target 608 and the deposition preventive board 602.